Refactor C++ language extensions and C++ support #3673

MKKnorr · 2024-11-15T14:09:34Z

No description provided.

neon60 · 2024-11-24T17:43:27Z

@MKKnorr Please rebase on docs/develop.

docs/how-to/hip_cpp_language_extensions.rst

randyh62

Looks ok to me. I left a few comments.

docs/how-to/hip_cpp_language_extensions.rst

randyh62 · 2024-11-27T00:30:47Z

docs/how-to/hip_cpp_language_extensions.rst

+HIP supports ``__threadfence()``, ``__threadfence_block()`` and
+``__threadfence_system()``.
+
+On AMD devices, ``__threadfence_system()``, has restrictions and therefore needs


This feels like it is referring to some implicit knowledge the user must have relative to threadfence_system? What are the "restrictions"? And is it appropriate to call it a workaround in the docs? Seems like a workaround is good for an issue or bug report, but not for user docs. Perhaps "requires the following process"?

I wish I had more information on this, but I couldn't find information proving or disproving this, so I just reformatted the already existing content

requires the following process?

I'll ask around what the current status on this feature is, maybe we can get rid of this section altogether, but I'll postpone it for now

docs/how-to/kernel_language_cpp_support.rst

cjatin · 2024-12-13T15:31:02Z

docs/how-to/hip_cpp_language_extensions.rst

+
+.. code-block:: cpp
+
+  #include <hip/hip_runtime.h>


can we modify this to add host and device functions as well?

This example is specifically about launching a kernel and I'd like to keep it as concise as possible

Make sense, but this kind of felt like a build up, there is description of host, device and global functions but example only shows global function. I think user reading through it, when they reach this section should get a complete picture of all three in action.

I'll leave it up to you, but if I was reading this, I wish there would be a more complete example which encompasses all that I just read.

docs/how-to/hip_cpp_language_extensions.rst

cjatin · 2024-12-13T15:37:30Z

docs/how-to/hip_cpp_language_extensions.rst

+
+GPU multiprocessors have a fixed pool of resources (primarily registers and
+shared memory) which are shared by the actively running warps. Using more
+resources can increase IPC of the kernel but reduces the resources available for


can increase IPC of the kernel

What does IPC mean here?

instructions per cycle. Rephrased the sentence to replace the acronym

Should we use such words (IPC incase of kernels?). Can we measure IPC for kernels? I would recommend using something like 'occupancy' which is a measurable metric.

cjatin · 2024-12-13T15:46:05Z

docs/how-to/hip_cpp_language_extensions.rst

+automatically reduce shared memory usage. The compilation fails, if the compiler
+can not generate code that satisfies the launch bounds.
+
+On NVCC this parameter maps to the ``.maxntid`` PTX directive.


If we are mentioning PTX directive, should we also mention the amdgpu_flat_work_group_size function attribute?

I agree, but this also is not the appropriate place in general. I already opened an issue to move this to the compiler documentation, as this does not directly relate to the language

cjatin · 2024-12-13T15:58:01Z

docs/how-to/hip_cpp_language_extensions.rst

+Porting from CUDA __launch_bounds
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+CUDA defines the ``__launch_bounds`` qualifier which works similar to


Does CUDA support __launch_bounds (without the trailing underscore?) can you point me to the CUDA documentation for it, cant seem to find it.

I could have sworn I've seen it somewhere, but it seems you're right, it also has trailing underscores. Fixed it.

docs/how-to/hip_cpp_language_extensions.rst

cjatin · 2024-12-13T16:06:17Z

docs/how-to/hip_cpp_language_extensions.rst

+Managed memory is a special qualifier, that makes the marked memory available on
+the device and on the host. For more details see :ref:`unified_memory`.
+
+__restrict__


Isnt restrict more of a clang extension than HIP, should we include it in HIP documentation? or alteast mention that here?

It is somewhat of a language extension, but also compiler specific/a hint to the compiler. However since CUDA requires this, I'm quite sure HIP also has to support it, so I'd say it has its place in this documentation

cjatin · 2024-12-13T16:17:10Z

docs/how-to/kernel_language_cpp_support.rst

+reduced support of the C++ standard library in device code, as functions are
+only compiled for the host by default. There are ongoing efforts to implement
+C++ standard library functionality with `libhipcxx
+<https://github.com/ROCm/libhipcxx>`_.


Something worth mentioning here, that STL features which are guaranteed to resolve at compile time (for example type_traits) are supported on device code.

That is also noted under C++11 support - constexpr, but I added an additional note here.

MKKnorr force-pushed the refactor-cpp-language-extensions branch 2 times, most recently from e911a63 to da93aea Compare November 15, 2024 14:34

neon60 force-pushed the hip_runtime_api_how-to branch from 0c52420 to 31fa125 Compare November 18, 2024 16:16

neon60 deleted the branch docs/develop November 18, 2024 17:39

neon60 closed this Nov 18, 2024

neon60 reopened this Nov 18, 2024

MKKnorr changed the base branch from hip_runtime_api_how-to to docs/develop November 19, 2024 09:34

MKKnorr force-pushed the refactor-cpp-language-extensions branch 2 times, most recently from 760259e to 6d6c430 Compare November 21, 2024 17:01

MKKnorr marked this pull request as ready for review November 21, 2024 17:01

MKKnorr requested review from chrispaquot, gandryey, saleelk, mangupta and rakesroy as code owners November 21, 2024 17:01

MKKnorr requested a review from neon60 November 21, 2024 17:02

MKKnorr force-pushed the refactor-cpp-language-extensions branch 3 times, most recently from 058fdde to 3eddfa4 Compare November 22, 2024 10:43

MKKnorr changed the base branch from docs/develop to landing_page_2 November 22, 2024 10:43

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neon60 force-pushed the landing_page_2 branch from 21b4cb3 to 021e579 Compare November 22, 2024 17:14

neon60 reviewed Nov 25, 2024

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MKKnorr force-pushed the refactor-cpp-language-extensions branch from 00a1e34 to b91f075 Compare December 4, 2024 11:28

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Docs: Refactor cpp_language_extensions and cpp_language_support

e9a6c15

neon60 force-pushed the refactor-cpp-language-extensions branch from 92410f6 to e9a6c15 Compare December 19, 2024 17:42

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Refactor C++ language extensions and C++ support #3673

Refactor C++ language extensions and C++ support #3673

MKKnorr commented Nov 15, 2024

neon60 commented Nov 24, 2024

randyh62 left a comment

randyh62 Nov 27, 2024

MKKnorr Nov 28, 2024

randyh62 Dec 2, 2024

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Refactor C++ language extensions and C++ support #3673

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Refactor C++ language extensions and C++ support #3673

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